Aneurysms are permanent distensions of the wall of a blood vessel, e.g., an artery, which disrupt the haemodynamics of the blood vessel. The aneurysm may halt the flow of blood at certain regions of the blood vessel, increasing the risk of clot formation, which may in turn cause a cerebral embolism. Furthermore, a reduction in the structural wall integrity of the blood vessel may occur, which can cause a reduction in the effectiveness of the blood vessel and put a higher strain on the heart muscle, increasing the risk of heart failure or vessel rupture.
Dissections are tears in the blood vessel's intima or delaminations of the collagen/elastin wall architecture of the blood vessel. Dissections can result in a false lumen, i.e., inner cavity, within the blood vessel. The false lumen may provide areas in which blood can pool, increasing the risk of clot formation and subsequent cerebral embolism. Severe dissection may even result in a breach of the blood vessel integrity and possible bleeding from the blood vessel e.g., into the thoracic cavity, which may cause death in a short period of time.
Traditional treatment for dissections and aneurysms include surgical resection, removing the offending tissue (depending on the extent of the damage to the blood vessel), or the insertion of a tubular prosthesis or stent grant within the lumen of the blood vessel to remove the mechanical loading on the damaged blood vessel wall and to provide a haemodynamically-compatible conduit for the transport of blood. Prostheses are traditionally made from Dacron® or high density Polytetrafluoroethylene (PTFE).
More recently, endovascular methods of prosthesis introduction have reduced health risks to the patient by allowing percutaneous introduction of the prosthesis via the femoral artery. Operations can therefore be conducted under local anaesthetic, and cardiac arrest and/or cardiac bypass procedures may be eliminated, reducing the overall cost of the treatment.
Prostheses and stent grafts have been designed for positioning at bifurcation regions of blood vessels, i.e., regions in which the blood vessel branches. For example, PCT Application nos. W000042948, W003082153 and W005122957 and U.S. Pat. No. 5,984,955 disclose bifurcated prostheses/stent grafts for positioning primarily at the iliac bifurcation of the aorta. The prostheses comprise a main conduit, a first branch conduit extending therefrom, and a removable or retractable second branch conduit. The main conduit is designed to locate within the aorta and the first and second branch conduits are designed to locate within respective iliac arteries.
Journal article: K. Inoue et al, Aortic Arch Reconstruction by Transluminally Placed Endovascular Branched Stent Graft,” Circulation, 1999; 100 describes a stent graft which includes conduits for aortic branches and a method of introduction.
The prostheses/stent grafts described above are generally sited percutaneously using a catheter delivery system which allows introduction to and guidance through the vasculature. Control of the device is made through pushrods or hypotubes which can extract the device from a casing and locate it in position.
Notably, none of these prostheses and stent grafts, or the delivery systems thereof, are intended for, or are indeed appropriate for, positioning at the branch region of the ascending aorta where the aortic root meets the right and left coronary arteries, which feed the heart muscle with oxygenated blood. The anatomy of the aortic root and the coronary arteries is complex. This location is particularly prone to aneurysms and dissections.